/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.log4j.helpers;

import java.util.Date;
import java.util.Calendar;
import java.util.TimeZone;
import java.text.FieldPosition;
import java.text.ParsePosition;
import java.text.DateFormat;

/**
 * Formats a {@link Date} in the format "HH:mm:ss,SSS" for example,
 * "15:49:37,459".
 * 
 * @author Ceki G&uuml;lc&uuml;
 * @author Andrew Vajoczki
 * @since 0.7.5
 */
public class AbsoluteTimeDateFormat extends DateFormat {
	private static final long serialVersionUID = -388856345976723342L;

	/**
	 * String constant used to specify
	 * {@link org.apache.log4j.helpers.AbsoluteTimeDateFormat} in layouts.
	 * Current value is <b>ABSOLUTE</b>.
	 */
	public final static String ABS_TIME_DATE_FORMAT = "ABSOLUTE";

	/**
	 * String constant used to specify
	 * {@link org.apache.log4j.helpers.DateTimeDateFormat} in layouts. Current
	 * value is <b>DATE</b>.
	 */
	public final static String DATE_AND_TIME_DATE_FORMAT = "DATE";

	/**
	 * String constant used to specify
	 * {@link org.apache.log4j.helpers.ISO8601DateFormat} in layouts. Current
	 * value is <b>ISO8601</b>.
	 */
	public final static String ISO8601_DATE_FORMAT = "ISO8601";

	public AbsoluteTimeDateFormat() {
		setCalendar(Calendar.getInstance());
	}

	public AbsoluteTimeDateFormat(TimeZone timeZone) {
		setCalendar(Calendar.getInstance(timeZone));
	}

	private static long previousTime;
	private static char[] previousTimeWithoutMillis = new char[9]; // "HH:mm:ss."

	/**
	 * Appends to <code>sbuf</code> the time in the format "HH:mm:ss,SSS" for
	 * example, "15:49:37,459"
	 * 
	 * @param date
	 *            the date to format
	 * @param sbuf
	 *            the string buffer to write to
	 * @param fieldPosition
	 *            remains untouched
	 */
	public StringBuffer format(Date date, StringBuffer sbuf,
			FieldPosition fieldPosition) {

		long now = date.getTime();
		int millis = (int) (now % 1000);

		if ((now - millis) != previousTime) {
			// We reach this point at most once per second
			// across all threads instead of each time format()
			// is called. This saves considerable CPU time.

			calendar.setTime(date);

			int start = sbuf.length();

			int hour = calendar.get(Calendar.HOUR_OF_DAY);
			if (hour < 10) {
				sbuf.append('0');
			}
			sbuf.append(hour);
			sbuf.append(':');

			int mins = calendar.get(Calendar.MINUTE);
			if (mins < 10) {
				sbuf.append('0');
			}
			sbuf.append(mins);
			sbuf.append(':');

			int secs = calendar.get(Calendar.SECOND);
			if (secs < 10) {
				sbuf.append('0');
			}
			sbuf.append(secs);
			sbuf.append(',');

			// store the time string for next time to avoid recomputation
			sbuf.getChars(start, sbuf.length(), previousTimeWithoutMillis, 0);

			previousTime = now - millis;
		} else {
			sbuf.append(previousTimeWithoutMillis);
		}

		if (millis < 100)
			sbuf.append('0');
		if (millis < 10)
			sbuf.append('0');

		sbuf.append(millis);
		return sbuf;
	}

	/**
	 * This method does not do anything but return <code>null</code>.
	 */
	public Date parse(String s, ParsePosition pos) {
		return null;
	}
}
